Development of the age-related spontaneous spike-wave discharges in rat neocortex and exposure to a model neurotoxin

In laboratory rats an epileptic-like spontaneous neocortical activity in the form of bursts of spike and wave discharges (SWD) develops gradually with age. High incidence of the SWD episodes is accompanied by other indices characteristic of advanced age: memory disturbances and atrophic changes within basal forebrain structures (Buzsaki et al. 1988b, Gage et al. 1988). Accordingly, it has been proposed that the number and duration of the SWD episodes be regarded as a diagnostic marker to distinguish between young and old brains (Buzsaki et al. 1988a). It is suspected that exposure to neurotoxins may accelerate the progress of age-related neurodegeneration by predisposing neurons to premature death and thus hasten the appearance of the age-related functional deficits (Weiss 1990). Analysing the development of SWD activity in exposed rats may be helpful for an assessment of the potency of the neurotoxin under study to exert such an effect. In the present work the influence of a three-month exposure to a model neurotoxin, ethanol (ETOH), on the development of the SWD activity in imp-DAK rats was investigated. It has been found that in rats given 10% ETOH solution as the only drink for three months, the incidence of the SWD episodes increased markedly. The increase was most clearly seen after ETOH withdrawal and on the 90th day after exposure no tendency to decline could be observed. The obtained data indicate that exposure to exogenous substances may exert a distinguishable long-lasting influence on the development of the SWD activity.